1. Field of the Invention
The present invention relates to polyurethanes containing amide groups in the backbone of the polyurethane; to one-component, thermoset compositions containing these polyurethanes and a cross-linking component; and to coatings, sealants and adhesives prepared from these compositions.
2. Description of the Prior Art
One-component polyurethane coating compositions containing polyisocyanates blocked with reversible, monofunctional blocking agents for isocyanate groups and polyols are an important class of materials for applications such as automotive OEM coatings. While these one-component compositions overcome the difficulties of two-component coating compositions with regard to accurate metering of the components, the one-component coating compositions also have disadvantages, which are primarily caused by the volatilization of the blocking agent.
The release of the blocking agent can cause blistering and yellowing in thick films and oven fouling. In addition, the blocking agents are considered to be volatile organic compounds (VOC""s) in the same manner as organic solvents. Therefore, certain coating compositions may not satisfy environmental regulations solely due to the presence of blocking agents.
It is an object of the present invention to overcome the known disadvantages of one-component coating compositions caused by the release of blocking agents during cure without affecting the advantages of these coating compositions when compared to two-component coating compositions.
These objects can be achieved with the one-component compositions according to the present invention, which are based on polyurethanes containing amide groups in the backbone of the polyurethane and crosslinking agents that are reactive with amide groups. These compositions do not require blocking agents and, thus, do not release blocking agents. When the one-component compositions according to the invention are cured, the only compounds released are water or monoalcohols, which are much less toxic than conventional blocking agents.
U.S. Pat. No. 5,780,559 discloses polyurethanes containing amide groups; however, the amide groups are present in terminal positions as opposed to being present in the backbone. A teaching of the presence of amide groups in terminal positions would not suggest their use in the backbone, especially in view of the comparison examples set forth hereinafter. These examples demonstrate that amide groups in pendant positions are not suitable for use in one-component thermoset compositions because they separate into two phases in the presence of common lacquer solvents.
The present invention relates to polyurethanes containing an average of at least two secondary amide groups in the backbones of the polyurethanes, wherein the secondary amide groups (calculated as NHxe2x80x94COxe2x80x94, MW 43) are present in an amount of 1 to 14% by weight, based on the weight of the polyurethanes, and correspond to the formula
xe2x80x94X1xe2x80x94R1xe2x80x94NHxe2x80x94C(O)xe2x80x94R2xe2x80x94X2xe2x80x94xe2x80x83xe2x80x83(I) 
wherein
X1 and X2 are the same or different and represent the groups obtained by removing a hydrogen atom from a hydroxy group or a primary or secondary amino group and
R1 and R2 are the same or different and represent linear or branched hydrocarbon groups that are optionally substituted by groups that do not contain isocyanate-reactive hydrogen atoms.
The present invention also relates to one-component, thermoset compositions containing the polyurethanes with secondary amide groups in the backbone and a cross-linking component that is reactive with amide groups. Finally, the present invention relates to coatings, sealants and adhesives prepared from these one-component, thermoset compositions.